LAUSR

Purpose This paper aims to achieve the following objectives. First, through a longitudinal study, the authors explore the trend of voluntary external assurance of sustainability reports among Italian listed companies from 2008 to 2012. Thus, the authors aim to analyse the content level of the assurance statements and to test whether it is affected by certain corporate variables and by the type of practitioner chosen. Design/methodology/approach A legitimacy theory framework is adopted to investigate the phenomenon of sustainability report assurance services in Italy. The authors developed an assurance statement disclosure index (ASDI) constructed on the basis of the standards ISAE 3000 and AA1000AS. Thus, the authors tested whether the ASDI is affected by certain corporate variables using an ordinary least square (OLS) regression model. To test how each specific item is related to the assurance provider, a contingency table was developed. Findings The results of this paper show many differences in the assurance statements content in particular with reference to the criteria used, conclusive comments and recommendations. The presence of a corporate social responsibility committee and an expert who serves on it is positively related to a higher rank on the ASDI. In contrast, Big4 firms seem to be associated with a lower disclosure rank. Finally, Big4 are positively associated with the indications of the provider’s characteristics and negatively with their conclusive comments and recommendations. Originality/value This paper presents some findings in an area where little evidence exists, that is, the effects of some variables on the quantity of information disclosed in the assurance statements.